1. Field of the Invention
The present invention relates to a method of manufacturing a liquid ejection head, and more particularly to a method of manufacturing a liquid ejection head in which droplets of liquid are ejected from a nozzle connected to a pressure chamber by supplying liquid from a liquid supply channel to the pressure chamber and then applying pressure to the liquid inside the pressure chamber.
2. Description of the Related Art
A liquid ejection head (inkjet head) has been known in which ink is supplied to a pressure chamber from an ink tank via an ink supply channel, pressure is generated inside the pressure chamber by a pressure generating device, such as a piezoelectric element, and ink is thereby ejected from a nozzle (ejection port) connected to the pressure chamber.
Moreover, an inkjet recording apparatus (inkjet printer) has been known which includes an inkjet head having a plurality of nozzles and which forms an image on a recording medium by ejecting ink droplets towards the recording medium from the plurality of nozzles in the inkjet head, while moving the inkjet head described above and the recording medium relatively to each other.
In this way, in an inkjet recording printer, an image is formed by combining ink dots composed of ink droplets ejected from the nozzles and deposited on the recording medium. In recent years, there have been demands for increased image quality in an image (inkjet print) produced by the inkjet printers to the extent that the image quality of the inkjet print surpasses an image quality of a photographic print.
In response to these demands, various proposals have been made in the related art to arrange the nozzles and the pressure chambers connected to the nozzles at high density, and to form the supply channels, and the like, which supply ink to the pressure chambers, with high accuracy.
For example, Japanese Patent Application Publication No. 07-132595 discloses an inkjet head having a plurality of ink pressure chambers each of which has one end connected to an ink pool unit via an ink supply channel and has the other end connected to a nozzle which ejects ink droplets. In this inkjet head, each of the ink supply channels is defined by at least two wall faces being parallel to a Si(111) plane that is inclined with respect to the surface of a (110) silicon substrate (i.e., monocrystalline (singular-crystalline) silicon substrate whose surface is parallel to a Si(110) plane). Moreover, each of the pressure chambers is defined by at least two walls being parallel to a Si(111) plane that is perpendicular with respect to the surface of the (110) silicon substrate.
This method of manufacturing the inkjet head disclosed in Japanese Patent Application Publication No. 07-132595 is described below with reference to FIG. 16.
FIG. 16 is a plan diagram showing an enlarged view of the ink pool unit, the pressure chamber and the supply channel that are formed in the monocrystalline silicon substrate. A monocrystalline silicon substrate 100, whose surface is parallel to a Si(110) plane, is subjected to a thermal oxidation process, and the like, and is thereby covered with a film 200 of silicon oxide (i.e., Si oxide). The silicon oxide film 200 is selectively etched away, resulting in the formation of an etching mask composed of the silicon oxide film 200 on the monocrystalline silicon substrate 100. Thereupon, anisotropic wet etching is carried out using the etching mask of the silicon oxide film 200, thereby forming a cavity for a pressure chamber 101, a cavity for an ink pool unit 103, and a supply channel 102, as shown in FIG. 16. In this case, the pressure chamber 101 is defined by four walls: two of which are parallel to a Si(111) plane that is perpendicular to the surface of the monocrystalline silicon substrate 100; and the others (two walls having a forward-taper shape shown in FIG. 16) of which are parallel to a Si(111) plane that is inclined with respect to the monocrystalline silicon substrate 100. By continuing the wet etching process further, the forward-taper shaped walls (shown in FIG. 16) that are parallel to the Si(111) plane that is inclined with respect to the silicon substrate 100 disappear as the anisotropic etching progresses. Finally, the partition 204a between the pressure chamber 101 and the supply channel 102, and the partition 204b between the ink pool unit 103 and the supply channel 102 are etched by isotropic wet etching, thereby connecting the pressure chamber 101 with the supply channel 102, and the supply channel 102 with the ink pool section 103. In this isotropic etching operation, the film 200 of silicon oxide is also removed at the same time.
In the above-described method of manufacturing an inkjet head, the depth of the supply channel 102 is dependent on the width of the openings of the etching mask, and the accuracy of the shape and dimensions of the supply channel 102 is sought to be achieved as described above.
However, in the method for manufacturing the inkjet head described above, since the silicon substrate 100 is immersed in a wet etchant (liquid for wet etching) for a long period of time in order to remove the forward-taper shaped walls that are parallel to the Si(111) plane and define the cavity for the pressure chamber 101, then side etching proceeds below the etching mask, the (111) faces defining the recess sections of the supply channels 102 retreat, and the dimensions of the supply channels 102 diverge from the design values. Furthermore, generally, there is fluctuation in the wet etching rate within the same plane of a substrate, and hence there is a problem in that it is difficult to achieve dimensional accuracy.
Moreover, in the method of manufacturing an inkjet head described above, the previously formed supply channel 102 is subjected to isotropic wet etching together with the partitions 204a and partitions 204b when the isotropic wet etching process is carried out, the shape of the supply channel 102 is changed to an isotropic shape, and therefore it is difficult to maintain the original shape (anisotropic shape) of the supply channel 102. Furthermore, due to the same reason as that stated above, it is difficult to achieve dimensional accuracy.
As described above, it is difficult to guarantee the shape, dimensions and dimensional accuracy of the flow channels after processing the flow channels, and hence fluctuation in the ink ejection characteristics arises. In particular, if the supply channel 102 is used as a supply restrictor (resistance flow channel section; also referred to as a “restrictor”), then this has significant effects on the ejection characteristics.
In the above-described method, by making the thickness of the partitions 204a and 204b the same as the thickness of the silicon oxide film 200 used as an etching mask, the silicon oxide film 200 is removed together with the partitions 204a and 204b when the isotropic wet etching is carried out. However, there often arises fluctuation in the etching rate within the same plane of the substrate, and therefore the fluctuation may arise in the etching rate between the partitions and the silicon oxide film. If the fluctuation arises in the etching rate between them, then there is a high possibility in that the substrate below the silicon oxide film 200 (namely, the portion of the silicon substrate that is not intended to be etched) is unintentionally etched away. Consequently, there is a problem in that the desired shape cannot be obtained, thereby adversely affecting the ejection characteristics.